Audio amplifier

ABSTRACT

An audio amplifier may comprise a signal limiting circuit and a power amplifier. The signal limiting circuit may be configured to limit an audio signal received at an input and to provide it as a limited audio signal at an output. The power amplifier may have a supply connection which may be coupled to a power supply unit in order to supply power to the power amplifier. The power amplifier may be configured to amplify a signal, which may be based on the limited audio signal, and to provide it as a level-limited audio signal at an output which may be coupled to a load, so that the load may be operated at limited power. The signal limiting circuit may be configured to produce an audio signal which may be limited depending on the load.

RELATED APPLICATION

This application corresponds to German Patent Application 10 2011 054060.1, filed on Sep. 29, 2011, at least some of which may beincorporated herein.

BACKGROUND

An audio amplifier may comprise a power amplifier and e.g. a powersupply unit. For some years, some audio amplifiers have also beenequipped with signal processing units known as digital signal processors(DSPs). Demands on the possible output power of audio amplifiers forprofessional use are increasing. Audio signals may be pulsed, and mayhave high peak values with a simultaneously relatively low RMS value. Asa result, high powers demanded from audio amplifiers may merely beneeded for a relatively short time. This property is taken into accountwhen designing power electronics assemblies for an audio amplifier, andsaid power electronics assemblies are thus able to deliver high voltagesand currents on a short-term basis. On a permanent basis, these highpowers may overtax the power electronics assemblies, which can bedestroyed on account of overheating, for example. A current supply lineis normally protected from overload by a circuit breaker, which maydisconnect the supply of current and hence the audio amplifier in theevent of excessive loading.

In order to inhibit the power electronics assemblies of an audioamplifier from being destroyed, it may be useful to provide for power tobe reduced in the course of operation when the power becomes excessive.This may be accomplished by using power supply units in which the outputvoltage falls under load. This may decrease the supply voltage for thepower amplifier, and the maximum output voltage of the power amplifiermay be reduced.

However, a disadvantage in this case may be that the power reduction mayaffect the tonal properties of the audio amplifier, specificallydepending on the load-dependent power supply unit used. A furtherdisadvantage may be that merely specific load-dependent power supplyunits matched to the characteristics of the amplifier may be used.

SUMMARY

Therefore, it may be useful to provide an audio amplifier which hasprotection against excessive output power. In particular, it may beuseful for the audio amplifier to be configured to be operable withpower supply units in which the output voltage does not fall under load.

It may further be useful to emulate the fall in the output voltage ofthe power supply unit under load in a signal limiting circuit connectedupstream of the power amplifier, so that the audio signal entering thepower amplifier is already limited depending on the load and hence thereis no longer any need for a power supply unit that performs theload-dependent limiting.

Hence, the audio amplifier may, for example, also be operated with apower supply unit in which the output voltage does not fall under load,and an output signal which is reduced under load may be produced, asrequired. Thus, the demands on the power supply unit may be decoupledfrom the demands on the signal limiting, which may be taken into accountby a suitable design of the signal limiting circuit. Hence, whendesigning the power supply unit, it may no longer be necessary to takeinto consideration disadvantageous influencing of the tonal propertiesduring signal limiting. A further advantage may be that when thecomponents of the signal limiting circuit are implemented in software,for example on a digital signal processor (DSP), the hardware componentsof the audio amplifier may, for example, be designed independently ofthe design of the software which brings about the signal limiting.

In an embodiment, the signal limiting circuit may, for example, compriseor be comprised in a digital signal processor (DSP), and the fall in theoutput voltage from the power supply unit may be calculated in the formof a model in the DSP. Specifically, a model of a (load-dependent) powersupply unit may be programmed into the DSP of the audio amplifier. Thepower, which may be output by one or more audio channels, may becaptured by the DSP, and the state of the power supply unit model may becalculated in real time. The design of the model may allow a fallingoutput voltage from a power supply unit to be simulated and hence theoutput power to be reduced. This concept may allow for the design ofaudio amplifiers with a briefly high output power even with power supplyunits in which the output voltage does not fall under load, for example,because they are corrected (e.g. regulated).

Furthermore, the tonal influences of the power reduction may no longerbe dependent on the actual physical power supply unit that is used, butrather may now be dependent (e.g. merely) on the design of the modelwhich is in the DSP. This may simplify porting a desired tonal responseto other audio amplifiers, or replacing the power supply unit within anappliance (e.g., an audio amplifier) with another without having toaccept tonal influences.

DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide an understanding ofembodiments, and together with the description, serve to explainprinciples of embodiments.

FIG. 1 is a block diagram of an audio amplifier based on an exemplaryembodiment.

FIG. 2 is a block diagram of an audio amplifier based on an exemplaryembodiment.

FIG. 3 is a block diagram of a digital signal processor in an audioamplifier based on an exemplary embodiment.

FIG. 4 is a block diagram of a digital signal processor in an audioamplifier based on an exemplary embodiment.

FIG. 5 is a block diagram of a digital signal processor in an audioamplifier based on an exemplary embodiment.

FIG. 6 is a schematic illustration to explain a method for amplifying adigital audio signal based on an exemplary embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary block diagram of an audio amplifier 100.The audio amplifier 100 may comprise a signal limiting circuit 101 and apower amplifier 103. The signal limiting circuit 101 may have an input140, in order to receive an audio signal 120, and/or an output 142, inorder to provide a limited audio signal 150 at said output. The audioamplifier 100 may be coupled to an audio source 132, which may emit anaudio signal which may be received by the signal limiting circuit 101 asan audio signal 120.

The audio signal 120 may be limited in the signal limiting circuit 101depending on the load. For example, driving a load 122 (e.g., aloudspeaker or a loudspeaker array) with a signal that is based on thelimited audio signal 150 may involve the limited audio signal 150 beingreduced in the event of excessively high powers appearing. This maycorrespond to the response of a power supply unit in which the outputvoltage falls under load. When a load 122 is operated on the audioamplifier 100, the output power of said load may therefore be reduced incomparison with an audio amplifier without signal reduction, which meansthat the load may effectively be prevented from being destroyed ordamaged. The load-dependent limiting of the audio signal 120 can beadjusted in the signal limiting circuit 101 by a model of a power supplyunit in which the output voltage falls under load, as illustrated by theexemplary block diagrams illustrated in FIGS. 3, 4 and 5. This mayvirtually relocate the load-dependent characteristic of such a powersupply unit into the signal limiting circuit 101, as a result of whichthe power amplifier 103 may be operated with any desired power supplyunit 102, particularly including the power supply units in which theoutput voltage does not fall under load (e.g., because they have acontrol loop which counteracts such a response). The signal limitingcircuit 101 may promote that when the load 122 is applied, the limitedaudio signal 150 is effectively limited depending on the load 122.

The signal limiting circuit 101 may comprise a digital signal processorwhich may receive a digital audio signal 120 and may limit the digitalaudio signal 120 to the limited audio signal 150, which may then beavailable as a limited digital audio signal 150. The signal limitingcircuit 101 may comprise a digital microcontroller or microprocessorwhich may receive a digital audio signal 120 and may limit the digitalaudio signal 120 to the limited audio signal 150, which may then beavailable as a limited digital audio signal 150. The signal limitingcircuit 101 may also comprise a digital signal processor and/or adigital microcontroller, which may together limit the digital audiosignal 120 to the limited audio signal 150. In these cases, theload-dependent limiting may already take place in the digital domainrather than in the analogue domain, as in ordinary audio amplifiers, andthe power loss on the analogue components may be reduced accordingly.

The signal limiting circuit 101 may also have one or more analoguecomponents which may receive an analogue audio signal 120 and limit theanalogue audio signal 120 to the limited audio signal 150, which maythen be available as a limited analogue audio signal 150. In an example,one or more analogue components may comprise one or more operationalamplifiers and/or comparators. In another example, analogue limiting canbe implemented by a comparator which may compare the analogue audiosignal 120 with a load-dependent threshold value and may performload-dependent limiting (e.g., based on the load-dependent thresholdvalue) in the event of said threshold value being exceeded.

The power amplifier 103 may receive a signal 152 which may be based onthe limited audio signal 150. A digital-to-analogue converter 108 mayoptionally be connected into the signal path between the signal limitingcircuit 101 and the power amplifier 103 to convert the limited audiosignal 150 provided by the signal limiting circuit 101 into the signal152. By way of example, such a digital-to-analogue converter 108 may benecessary when the signal limiting circuit 101 has a digital signalprocessor or a microprocessor which performs the limiting and/ordelivers a limited digital audio signal 150. Optionally, there may alsobe one or more other signal processing units connected in the pathbetween the signal limiting circuit 101 and the power amplifier 103,which may, for example, filter and/or average stages and/orpreamplifiers. In one or more configurations, however, the signal 152may be based on the limited audio signal 150 (e.g., such that thelimited audio signal 150 may be used to produce the signal 152). In anembodiment, the power amplifier 103 may be an analogue stage and thesignal 152 which the power amplifier 103 receives may be an analoguesignal. The power amplifier 103 may amplify the signal 152 based on thelimited audio signal 150 and may provide it as a level-limited audiosignal 154 (e.g., an audio signal that has the voltage level limited) atan output 146.

The audio signal 154 at the output of the audio amplifier 100 maytherefore be limited in voltage level so as to be able to operate theload 122 at limited power. That is, the voltage in the load 122 may beconverted into a power that is dependent on the load (e.g., on theimpedance of a loudspeaker), where the power limiting of the load mayresult as a consequence of the voltage limiting of the audio signal 154.

The power amplifier 103 may have a supply connection 144 which may becoupled to a power supply unit 102 to supply power to the poweramplifier 103. The power supply unit 102 may optionally be part of theaudio amplifier 100, but it may also be accommodated outside the audioamplifier 100, so that the supply connection 144 may be routed out ofthe audio amplifier 100 to allow the connection of an external powersupply unit. The power supply unit 102 may therefore be an assembly ofthe audio amplifier 100 in the first case, and it may be a standaloneappliance outside the audio amplifier 100 in the second case. The powersupply unit 102 may be used to supply power to the audio amplifier 100.For this purpose, the power supply unit 102 can be connected to a powersource (e.g., to the 220V or 110V AC mains and/or to a private powersupply system). The audio amplifier 100 may be designed such that itrequires a different power supply from that provided by the mains. Thevoltage conversion and/or the matching to the requirements of the audioamplifier 100 may be brought about by the power supply unit 102. Theoutput voltage and the maximum output current from the power supply unit102 may be permanently set or variable. The power supply unit 102 may bea switched-mode power supply unit and/or a transformer power supplyunit. In the case of the former, the power supply unit may be ofregulated or unregulated design.

The output 146 of the power amplifier may be coupled to a load 122, as aresult of which the load 122 can be operated with the level-limitedaudio signal 154 at limited power. Between the output 146 of the poweramplifier 103 and the load 122, there may also be further units, forexample power output stages or filter units, in the signal path.

The audio amplifier 100 may have a housing 124 which may accommodate thesignal limiting circuit 101 and/or the power amplifier 103. It may alsoaccommodate an optionally present digital-to-analogue converter 108and/or an optionally present (e.g., internal) power supply unit 102and/or also one or more other signal processing units, which may not beshown in FIG. 1.

The audio amplifier 100 described here may (e.g., also) be designedusing one or more power supply units in which the output voltages do notfall under load. Furthermore, the tonal properties of the powerreduction may no longer be dependent on the actual physical power supplyunit 102 used, but may rather now depend merely on the design of theload-dependent limiting in the signal limiting circuit 101. It maytherefore be possible to implement different tonal characteristics bychoosing an appropriate model of load-dependent limiting in the signallimiting circuit 101. A desired tonal response may therefore easily beported to other audio amplifiers 100. It may also be a simple matter forthe power supply unit 102 within an audio amplifier 100 to be replacedby another without having to accept tonal influences.

By way of example, the audio amplifier 100 may be used for audio signalamplification for one or more (e.g., powerful) loudspeakers which may beused for public addresses in large rooms or open areas. Suchloudspeakers may produce an acoustic power of over 50 watts,particularly over 100 watts, which, when a loudspeaker has an acousticefficiency of no more than 5%, for example, corresponds to electricalpowers of over 1000 watts, and particularly electrical powers of over2000 watts. The audio amplifier 100 may (e.g., also) be used for theaudio signal amplification in the case of loudspeaker arrays with amultiplicity of individual loudspeakers, in which relatively highacoustic powers in the region of multiples of 50 watts or 100 wattsarise. The audio signal to be amplified may be in the audible AF rangefrom approximately 20 Hz to 20 kHz and/or above.

FIG. 2 illustrates an exemplary block diagram of an audio amplifier 200.The audio amplifier 200 may have a DSP 201, a power amplifier 103, apower supply unit 102, two analogue-to-digital converters 104 a and 104b, a further digital-to-analogue converter 108, a digital input receiver107, a controller 105 and/or a user interface unit 106. The digitalinput receiver 107 may be connected between an analogue audio source 132and an input 140 of the DSP 201 in order to convert an analogue signal130 from the analogue audio source 132 into digital format and/or toprovide it for the DSP 201 at the input 140 thereof as a digital audiosignal 120. The digital-to-analogue converter 108 may be connectedbetween an output 142 of the DSP 201 and an input 148 of the poweramplifier 103 in order to make the limited audio signal 150 produced bythe DSP 201 available to the power amplifier 103 in analogue form as ananalogue signal 152. The power amplifier 103 may have a supplyconnection 144 which may be coupled to the power supply unit 102 toallow it to be supplied with the output voltage 156 from the powersupply unit 102. The power supply unit 102 may have a supply voltageinput which may be coupled to a supply voltage source 126.

The power supply unit 102 may be part of the audio amplifier 200 and maybe an assembly of the audio amplifier 200. The power supply unit 102 maybe used to supply power to the audio amplifier 200. For this purpose,the power supply unit 102 may be coupled to the supply voltage source126. By way of example, the supply voltage source may be the 220V or110V AC mains or a private power supply system. The audio amplifier 200may (e.g., usually) be designed such that it requires a different powersupply from that provided by the voltage supply source 126. The voltageconversion and the matching to the requirements of the audio amplifier200 may be brought about by the power supply unit 102. The outputvoltage and the maximum output current of the power supply unit 102 maybe permanently set and/or variable. The power supply unit 102 may be aswitched-mode power supply unit and/or a transformer power supply unit.In the case of the former, the power supply unit may be of regulatedand/or unregulated design.

The power amplifier 103 may have an output 146 coupled to a load 122 inorder, for example, to drive the load with the level-limited audiosignal 154. The analogue-to-digital converters 104 a and 104 b may beconnected between the output 146 of the power amplifier 103 and arespective control unit 148 a and 148 b of the DSP 201 in order, forexample, to provide the DSP 201 with the level-limited audio signal 154in digital form, wherein the analogue-to-digital converter 104 a mayconvert a current component and the analogue-to-digital converter 104 bmay convert a voltage component of the level-limited audio signal 154into digital form. The controller 105 may be coupled to the DSP 201 viaa configuration interface 160, may be coupled to the power supply unit102 via a control interface 162, may be coupled to the user interfaceunit 106 via a user interface 164 and/or may be coupled to the remotecontrol unit 128 via a remote control interface 166.

In an embodiment, the signal limiting circuit 101 from FIG. 1 is in theform of a digital signal processor (DSP) 201, and the power amplifier103 may correspond to the power amplifier 103 from FIG. 1. The receivedaudio signal 120 may be a digital audio signal which may be received atan input 140 of the DSP 201. The DSP 201 may limit the digital audiosignal 120 received at this input 140 and/or may provide it as a limiteddigital audio signal 150 at an output 142. In this embodiment, the input140 and the output 142 may be shown as an input and/or an output of theDSP 201. In other embodiments, in which the signal limiting circuit 101may comprise not merely the DSP 201 but also one or more other circuitunits, the input 140 and the output 142 may be inputs and/or outputs ofthe signal limiting circuit 101 which may be coupled to inputs and/oroutputs of the DSP 201 via the one or more other circuit units. Whilethe exemplary embodiment in FIG. 2 may relate to a DSP 201, the sameexplanations may apply, mutatis mutandis, even when, instead of the DSP201, a digital microcontroller and/or microprocessor may be used and/orwhen the functionality described here for the DSP 201 may be performed(e.g., both) by a DSP, a microcontroller, a microprocessor, and/orfurther digital hardware.

The DSP 201 may deliver a limited digital audio signal 150 at its output142. The power amplifier 103 may amplify a signal 152 which may be basedon the limited digital audio signal 150. The power amplifier 103 may bean analogue component which may receive an analogue signal 152 at aninput 148. To convert the limited digital audio signal 150 into ananalogue signal 152, a digital-to-analogue converter 108 which convertsthe limited digital audio signal 150 into the analogue signal 152 may beused (e.g., such that the analogue signal 152 may be based on thelimited digital audio signal 150). The block 108, which may be denotedas a digital-to-analogue converter, may also have one or more othercircuit units, such as, for example, one or more sampling rateconverters (e.g., one or more circuits for reducing and/or increasingthe sampling rate of the limited digital audio signal 150, so as to setany desired sampling rate for the limited digital audio signal 150),and/or one or more filter stages, which may (e.g., either) beimplemented in the digital-to-analogue converter 108 and/or connecteddownstream of the digital-to-analogue converter 108, in order toimplement a particular frequency response for the analogue signal 152based on the limited digital audio signal 150.

The power amplifier 103 may have a supply connection 144 which may becoupled to a power supply unit 102 and to which a power supply unit 102may be connected. The power supply unit 102 may, but does not have to,be one in which the output voltage 156 falls under load. By way ofexample, it may be a power supply unit 102 which delivers a constantoutput voltage 156, for example by virtue of internal control loopswhich may operate such that a sufficiently constant output voltage 156may be provided at the voltage output. The power supply unit 102 mayhave an input which may be coupled to a supply voltage source 126 whichmay deliver the supply voltage from which the power supply unit 102 mayproduce the output voltage 156 and may make it available to the poweramplifier 103 at the power supply input 144.

The input 140 of the digital signal processor 201 may receive a digitalaudio signal 120 which may be based on an audio signal 130 which may beprovided by an audio source 132. The audio source 132 may be a digitaland/or analogue audio source which may provide a digital audio signal130 and/or an analogue audio signal 130. In the case of a digital audiosource 132, the DSP 201 may have an upstream digital circuit unit 107 inthe form of a digital input receiver (DIR) which (e.g., if necessaryand/or requested) may perform sampling rate conversion for the digitalaudio signal 130 so as to produce a converted digital audio signal 120which may have a desired sampling rate so that it can be received by theinput 140 of the DSP 201. If the digital audio signal 130 already hasthe desired properties, the digital input receiver 107 can also beomitted, such that the digital audio signal 130 may be received directlyby the input 140 of the DSP 201.

In an embodiment of an analogue audio source 132, the DSP 201 may havean upstream analogue-to-digital converter 107 and/or optionally one ormore other (e.g., upstream) circuit units, where saidanalogue-to-digital converter may convert the analogue audio signal 130into a digital audio signal 120 which may be received by the input 140of the DSP 201. By way of example, the one or more other circuit unitsmay perform prefiltering on the analogue audio signal 130 (e.g.,low-pass filtering, high-pass filtering and/or bandpass filtering) sothat a filtered analogue audio signal 130 may be supplied to theanalogue-to-digital converter 107. If necessary (e.g., and/or requested,etc.), the output signal delivered by the analogue-to-digital converter107 may be subjected to sampling rate conversion and/or further digitalfiltering operations before it may be received at the input 140 of theDSP 201.

The audio amplifier 200 may have an analogue-to-digital converter 104 awhich may be arranged between the output 146 of the power amplifier 103and a control input 148 a of the DSP 201, and which may make thelevel-limited audio signal 154 produced by the power amplifier 103 atthe output 146 available to the DSP 201 in digital form. This may be thelevel-limited audio signal 154, as present on the load 122. The DSP 201may therefore have the opportunity to produce its limited audio signal150 in a manner dependent on the load, since coupling the output 146 ofthe power amplifier 103 to the load 122 may involve the level-limitedaudio signal 154 assuming a load-dependent value.

The level-limited audio signal 154 produced by the power amplifier 103may be measured using its current component and/or using its voltagecomponent. In the exemplary block diagram in FIG. 2, (e.g., both) thecurrent component and/or the voltage component may be measured, with theanalogue-to-digital converter 104 a converting a current component ofthe level-limited audio signal 154 into digital format and making itavailable to the DSP 201 at the control input 148 a. A furtheranalogue-to-digital converter 104 b, which may be arranged between theoutput 146 of the power amplifier 103 and a further control input 148 bof the DSP 201, may convert a voltage component of the level-limitedaudio signal 154 into digital format and may make it available to theDSP 201 at the further control input 148 b. Hence, the DSP 201 candetermine the limited audio signal 150 based on the power of thelevel-limited audio signal 154 and/or based on the power on the load122.

In another embodiment, the audio amplifier 200 may have (e.g., merely)one of the two analogue-to-digital converters 104 a and 104 b, as aresult of which merely one current component of the level-limited audiosignal 154 may be made available to the DSP 201, for example. Since aload-dependent value may be obtained for the current component of thelevel-limited audio signal 154 when the output 146 of the poweramplifier 103 is coupled to the load 122, the DSP 201 may be able toproduce the limited audio signal 150 depending on the load.

Alternatively (e.g., and/or additionally), in an embodiment with justone of the two analogue-to-digital converters 104 a and 104 b, it mayalso be possible for the voltage component (e.g., instead of the currentcomponent) to be made available to the DSP 201. However, the loaddependency of the voltage may merely be minimal and may be determinedprimarily by the internal resistance of the amplifier and/or the losseson the lines. As a result, the changes in the load 122 may becomenoticeable merely slightly in the voltage. It may therefore bepreferable to deliver the current component to the DSP 201 with just oneof the A/D converters 104 a and 104 b.

In a different embodiment, the audio amplifier 200 may have neither ofthe two analogue-to-digital converters 104 a and 104 b. In such anexemplary embodiment, information about the load 122, for exampleimpedance values for the load, and/or the power amplifier 103 may bemade available to the DSP 201, and may be used in the DSP 201 tocalculate how the limited audio signal 150 produced by the DSP 201 maybe converted into the level-limited audio signal 154 in order to drivethe load. This information may allow the DSP 201 to produce the limitedaudio signal 150 depending on the load.

The DSP 201 may produce the limited audio signal 150 on the basis of amodel 310 of a power supply unit in which the output voltage may fallunder load. Such a model, as described in more detail in the subsequentdiscussion related to FIGS. 3, 4 and/or 5, may be used to produce thelimited audio signal 150 depending on the load. As mentioned above, suchload-dependent power supply units in which the output voltage iscontrolled to fall under load are used as power supply units forconventional audio amplifiers in order reduce the maximum output voltageof the power amplifier. Thus, in accordance with the disclosure, thefunctionality of providing a level-limited audio signal is integratedinto the audio amplifier and may therefore e.g. be removed from the(formerly load-dependent) power supply unit.

The audio amplifier 200 may have a configuration interface 160 in orderto transmit control and/or configuration data between a controller 105or microprocessor and the DSP 201. The controller 105 may be coupled tothe power supply unit 102 via a control interface 162 in order to useone or more control commands to set the power supply unit 102 and/or torequest information from the power supply unit 102. The controller 105may be coupled to a user interface unit 106 via a user interface 164 inorder to use control commands to configure the controller 105 and/or toload code into it and/or to request information from the controller 105.The controller 105 may be coupled to a remote control unit 128 via aremote control interface 166 in order to use control commands toconfigure the controller 105 by remote control and/or to load code intoit and/or to request information from the controller 105 by remotecontrol.

The DSP 201 and the controller 105 may be produced as one circuit, whichmay correspond to the signal limiting circuit 101 from FIG. 1. Thefunctionality of the DSP 201 may be performed fully and/or in part bythe controller 105. Similarly, the functionality of the controller 105may be performed fully and/or in part by the DSP 201.

The audio amplifier 200 may have a housing 124 which may accommodate theDSP 201, the power amplifier 103, the power supply unit 102, at leastone of the analogue-to-digital converters 104 a and/or 104 b, thedigital-to-analogue converter 108, the digital input receiver 107, thecontroller 105 and/or the user interface unit 106.

The audio amplifier 200 may be used for audio signal amplification for(e.g., powerful) loudspeakers that may be used for public address inlarge rooms and/or open areas. Loudspeakers of this kind produce anacoustic power of over 50 watts, and often over 100 watts. The audioamplifier 200 may also be used for the audio signal amplification in thecase of loudspeaker arrays with a multiplicity of individualloudspeakers arranged above one another, in which relatively highacoustic powers in the region of multiples of 50 watts may arise. Theaudio signal to be amplified may be in the audible or just (e.g.,barely) inaudible AF range from approximately 20 Hz to 20 kHz and above.

FIG. 3 illustrates an exemplary block diagram of a digital signalprocessor 201 in an audio amplifier 200. The DSP 201 may correspond tothe DSP 201 described in FIG. 2. The DSP 201 may have a signal pathbetween the input 140 and the output 142, into which signal path a firstaudio processing unit 314, a peak value limiting unit 315 and/or asecond audio processing unit 316 may have been connected. The input 140may correspond to the input 140 shown in FIG. 2 for the DSP 201, atwhich the digital audio signal 120 may be received. The output 142 maycorrespond to the output 142 shown in FIG. 2, at which the limiteddigital audio signal 150 may be provided.

The DSP 201 may (e.g., also) have a control path between two controlinputs 148 a and 148 b of the DSP 201 and the peak value limiting unit315, where the control path may be used to actuate the peak valuelimiting unit 315 with a controlled variable 326. The two control inputs148 a and 148 b may correspond to the control inputs 148 a and 148 bdescribed in FIG. 2 for the DSP 201. The control path may have amultiplication unit 312, a modelling unit 310 and/or a control unit 311connected into it, wherein the modelling unit 310 may obtain its inputparameters for modelling a power supply unit in which the output voltageU_(C) falls under load from a parameter memory 313 and from themultiplication unit 312. The parameter memory 313 may use a parameterinterface to provide the modelling unit 310 with a first parameter C,which may correspond to a virtual capacitance, and with a secondparameter P_(in), which may correspond to a prescribable maximum inputpower for the power amplifier 103. The multiplication unit 312 mayprovide the modelling unit 310 with a third variable (directlycontrolled variable) P_(out) which may be variable in operation andwhich may correspond to an output power of the power amplifier 103. Themultiplication unit 312 comprises two inputs which may correspond to thecontrol inputs 148 a and 148 b of the DSP 201 and at which themultiplication unit 312 may receive a current component I and/or avoltage component V of the level-limited audio signal 154 produced bythe power amplifier 103 in digital form. From the voltage component Uand/or the current component I, the multiplication unit 312 may form theproduct, which may emulate a power P_(out) of the level-limited audiosignal 154 produced by the power amplifier 103. The multiplication unit312 may comprise an integrator, a summator and/or an averaging unit,which it may use to make an averaged power P_(out) available to themodelling unit 310.

The parameter memory 313 may be externally accessible via an externalconfiguration interface 160 which may be used to set and/or request theparameters C and P_(in) stored in the parameter memory 313. Theparameter memory 313 may be an internal memory in the DSP 201, as shownin FIG. 3. Alternatively, the parameter memory 313 may be an externalmemory which the DSP 201 may access via an external memory interface(e.g., such that the parameter memory 313 may be implemented outside theDSP 201, contrary to the illustration in FIG. 3).

The modelling unit 310 may emulate a model of a power supply unit inwhich the output voltage U_(C) may fall under load. The model maycomprise a virtual capacitance C which may be charged with the suppliedpower P_(in) and may be discharged with the drawn power P_(out). Whenthe output of the virtual capacitance C is connected to a load, thevirtual capacitance C may discharge, with a load-dependent dischargecurrent flowing and (e.g., at the same time) the output voltage U_(C)across the virtual capacitance C dipping. The output voltage U_(C) mayfall under load. If the supplied power P_(in) corresponds to the outputpower P_(out), a power equilibrium may establish itself on the virtualcapacitance C and the virtual capacitance may remain in the chargedstate. If the supplied power P_(in) is higher than the output powerP_(out), the virtual capacitance may be charged.

The model of the virtual capacitance may be suitable for implementingpower limiting control. So long as the drawn power P_(out) is less thanthe suppliable power P_(in), the output voltage U_(C) may assume itsmaximum value U₀.

The virtual capacitance C may tolerate (e.g., briefly occurring) highpower peaks in the drawn power P_(out), which may bring about partialdischarge of the virtual capacitance C. In the case of high RMS powersin the drawn power, on the other hand, the virtual capacitance may bedischarged to a high degree.

In one example, the output voltage U_(C) may fall merely slightly belowits maximum value, whereas in a different example, the output voltageU_(C) may quickly fall to one or more low values.

Depending on the desired output power P_(out), the supplied power P_(in)may be set such that a power equilibrium may be produced on the virtualcapacitance C. This may make it possible to implement a setting in whichbrief power peaks may be transmitted whereas high RMS power values maybe limited.

The supplied power P_(in) may be a constant parameter and may not changein the course of operation. U₀ may be an upper limit for the suppliablepower.

Such power limiting control may be implemented in the modelling unit310, wherein the supplied power P_(in) may correspond to a prescribedparameter which may specify the maximum input power on the virtualcapacitance C, and the output power P_(out) may denote the power whichmay actually be drawn for the load 122, which the multiplication unit312 may have calculated on the basis of the level-limited audio signal154 applied to the load 122.

On the basis of the output voltage U_(C), the control unit 311 maydetermine a controlled variable 326 which may be used to actuate thepeak value limiting unit 315. The peak value limiting unit 315 may beused to limit the power peaks in the digital audio signal 120 applied tothe input 140 by using the controlled variable 326. Specifically, thedigital audio signal 120 may enter the first audio processing unit 314,in which it may be subjected to digital filtering and/or to routing inorder to be received as a filtered digital audio signal 322 by the peakvalue limiting unit 315. In the peak value limiting unit 315, thefiltered digital audio signal 322 may be limited on the basis of thecontrolled variable 326 from the control unit 311, said limiting beingbrought about by reducing the signal level of the digital audio signal322. The limited filtered digital audio signal 324 produced in thismanner may enter the second audio processing unit 316, in which it maybe subjected to further digital filtering and/or further limiting andmay be provided at the output 142 of the DSP 201 as a limited digitalaudio signal 150. The further limiting may be independent of load (e.g.,limiting which matches the limited digital audio signal 150 to asubsequent digital-to-analogue converter 108).

In another embodiment, the DSP 201 may have no audio processing units314 and/or 316. In that case, the signal 120 may correspond to thesignal 322 and the signal 324 may correspond to the signal 150.Alternatively, the DSP 201 may have no first audio processing unit 314.In that case, the signal 120 may correspond to the signal 322.Alternatively, the DSP 201 may have no second audio processing unit 316.In that case, the signal 324 may correspond to the signal 150.

FIG. 4 illustrates an exemplary block diagram of a digital signalprocessor 201 in an audio amplifier 200. The DSP 201 may correspond tothe DSP 201 described in FIG. 2 and/or to the DSP 201 described in FIG.3.

For the model of a power supply unit in which the output voltage U_(C)falls under load, where the power supply unit is emulated in themodelling unit 310, the relationship described below may apply. Betweenthe energy W_(C) stored in the virtual capacitance C and the voltageU_(C) across the virtual capacitance C, the following relationship mayapply:

W _(C)=½·C·U _(C) ².

On the other hand, there may be a differential relationship betweenenergy and power. Thus, power may be the time derivation of energy andenergy may be power integrated with respect to time:

W _(C)=∫(P _(in) −P _(out))dt.

Hence, the right-hand sides of both equations correspond, and thefollowing relationship applies:

U _(C) =f(P _(out) ,P _(in) ,C).

FIG. 5 illustrates an exemplary block diagram of a digital signalprocessor 201 in an audio amplifier 200. The DSP 201 may correspond tothe DSP 201 described in FIG. 2 and/or to the DSP 201 described in FIG.3 and/or FIG. 4.

For the model of a power supply unit in which the output voltage U_(C)falls under load, where the power supply unit is emulated in themodelling unit 310, the relationship described below may apply. Betweenthe energy W_(C) stored in the virtual capacitance C and the voltageU_(C) across the virtual capacitance C, the following relationship mayapply:

W _(C)=½·C·U _(C) ².

On the other hand, there may be a differential relationship betweenenergy and power. Thus, power may be the time derivation of energy andenergy may be power integrated with respect to time:

W _(C)=∫(P _(in) −P _(out))dt.

If P_(in) and C are assumed to be constant, it may be possible tocalculate the voltage value U_(C) by observing the drawn power P_(out):

½·C·ΔU ²=∫(P _(in) −P _(out))dt

and from that:

ΔU ²=2/C·∫(P _(in) −P _(out))dt.

Bearing in mind an initial condition for U_(C), U_(C)(0)=U₀=constant,the following may be obtained:

U _(C) ² =U ₀ ² +ΔU ²

and hence:

U _(C)=√{square root over ( )}(U ₀ ² +ΔU ²).

The initial condition for U_(C), U_(C)(0)=U₀ may be stored in theparameter memory 313 as a prescribable parameter which may be suppliedto the modelling unit 310 via the parameter interface.

FIG. 6 illustrates an exemplary schematic that demonstrates a method foramplifying an audio signal 120. The method may have the acts indicatedbelow. In a first act 601, an audio signal 120 may be limited in orderto produce a limited audio signal (150). In a second act 603, a signal152 based on the limited audio signal 150 may be amplified in order toproduce a level-limited audio signal 154. In a third act 605, thelevel-limited audio signal 154 may be provided at an output 146 whichmay be coupled to a load 122, as a result of which the load 122 may beoperated at limited power because it is subject to level limiting. Inthis case, the limiting 601 may take place such that the limited audiosignal 150 may be limited depending on the load.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the claimed subject matter. This applicationis intended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisdisclosure be limited merely by the claims and the equivalents thereof.

What is claimed is:
 1. An audio amplifier, comprising: a signal limitingcircuit configured to: limit an audio signal received at an input; andprovide the limited audio signal at a first output; and a poweramplifier comprising a supply connection configured to be coupled to apower supply unit to supply power to the power amplifier, the poweramplifier configured to: amplify a signal based on the limited audiosignal; and provide the amplified signal as a level-limited audio signalat a second output configured to be coupled to a load, such that theload can be operated at limited power, the signal limiting circuitconfigured to produce an audio signal that is limited based on the load.2. The audio amplifier of claim 1, the load comprising at least one of aloudspeaker or a loudspeaker array.
 3. The audio amplifier of claim 1,the signal limiting circuit comprising at least one of a digital signalprocessor or a microcontroller.
 4. The audio amplifier of claim 1, thesignal limiting circuit configured to produce the audio signal based ona model of a load-dependent power supply unit associated with an outputvoltage falling under load.
 5. The audio amplifier of claim 1, thesignal limiting circuit configured to produce the limited audio signalbased on the level-limited audio signal provided at the second output.6. The audio amplifier of claim 1, comprising a digital-to-analogueconverter arranged in a signal path between the signal limiting circuitand the power amplifier.
 7. The audio amplifier of claim 1, furthercomprising the power supply unit, the power supply unit being coupled tothe supply connection of the power amplifier and configured to produce aload-independent output voltage.
 8. The audio amplifier of claim 1,comprising an analogue-to-digital converter arranged between the secondoutput and a control input of the signal limiting circuit, theanalogue-to-digital converter configured to provide a current componentof the level-limited audio signal for the signal limiting circuit. 9.The audio amplifier of claim 8, comprising a second analogue-to-digitalconverter arranged between the second output and a second control inputof the signal limiting circuit, the second analogue-to-digital converterconfigured to provide a voltage component of the level-limited audiosignal for the signal limiting circuit.
 10. The audio amplifier of claim1, the signal limiting circuit configured to determine the audio signalbased on a function of a prescribable maximum input power of the poweramplifier, an output power of the power amplifier and a virtualcapacitance.
 11. The audio amplifier of claim 10, the signal limitingcircuit configured to determine the output power of the power amplifierbased on a product of a current component and a voltage component of thelevel-limited audio signal.
 12. The audio amplifier of claim 10,comprising a configuration interface configured to adjust the virtualcapacitance and the prescribable maximum input power of the poweramplifier.
 13. A method for amplifying an audio signal, comprising:limiting the audio signal to produce a limited audio signal; amplifyinga signal based on the limited audio signal to produce a level-limitedaudio signal; and providing the level-limited audio signal at an outputconfigured to be coupled to a load, such that the load can be operatedat limited power, the limiting performed based on the load.
 14. Themethod of claim 13, the load comprising at least one of a loudspeaker ora loudspeaker array.
 15. The method of claim 13, the limiting based on amodel of a load-dependent power supply unit associated with an outputvoltage falling under load.
 16. The method of claim 15, the limitingperformed using the following formulae:U _(C)=√{square root over ( )}(U ₀ ² +ΔU ²).ΔU ²=2/C·∫(P _(in) −P _(out))dt, where P_(in) is a maximum prescribableinput power on a virtual capacitance C, P_(out) is an output power onthe virtual capacitance C, ΔU is a differential voltage change on thevirtual capacitance C, U₀ is an initial voltage on the virtualcapacitance C, and U₀ is the output voltage.
 17. The method of claim 15,the output voltage a basis for altering a threshold used to limit peakvalues of the audio signal.
 18. An audio amplifier, comprising: a signallimiting circuit configured to: limit an audio signal received at aninput; and provide the limited audio signal at a first output; and apower amplifier configured to: amplify a signal based on the limitedaudio signal; and provide the amplified signal as a level-limited audiosignal at a second output configured to be coupled to a load.
 19. Theaudio amplifier of claim 18, the power amplifier comprising a supplyconnection configured to be coupled to a power supply unit.
 20. Theaudio amplifier of claim 18, the signal limiting circuit configured toproduce an audio signal that is limited based on the load.